A diamond has sold for nearly 21.5 million US dollars (£13.5 million) - a world auction record price per carat for such a colourless stone.

Named for Archduke Joseph August of Austria, the great-grandson of both a Holy Roman emperor and a French king, the diamond passed to his son, Archduke Joseph Francis, who put it in a bank vault, then to an anonymous buyer who kept it in a safe during the Second World War.

From there it surfaced at a London auction in 1961, then at a Geneva auction in 1993, when Christie's sold it for 6.5 million dollars (£4 million).

It was sold in the latest Christie's Geneva jewellery auctions, held in five-star hotels along the Swiss city's lakefront, seemingly a continent if not a world away from the grim austerity gripping much of Europe.

The Archduke Joseph Diamond went for 21,474,525 dollars including commission at Christie's auction. That was well above the expected 15 million US dollars (£9.5 million) and more than triple the price paid for it at auction almost two decades ago.

The 76.02-carat diamond, with perfect colour and internally flawless clarity, came from the ancient Golconda mines in India.

The seller, Alfredo J Molina, chairman of California-based jeweller Black, Starr & Frost, said immediately afterwards there were two main bidders and that he was delighted with the result. Mr Molina said the winning bidder, who wished to remain anonymous, is going to donate the diamond for display at a museum.

"It's a great price for a stone of this quality," Mr Molina said. "It's one of a kind, so it's like saying 'Are you pleased when you sell the Mona Lisa?' Or 'Are you pleased when you sell the Hope Diamond?' It's all what the market will bear, and the stone sold for a very serious price."

Perhaps buyers were not entirely immune to the harsh financial climate in Europe - or at least some Geneva version of it. Two plus-sized diamonds did not sell, a yellow diamond with 70.19 carats failed to sell because the final bid was just below the reserve price and a 12.16-carat pink diamond did not sell because the final bid was well under the reserve price.